Knife rolls for making transverse separating cuts or cuts in the form of rows of perforations have become known in various different designs. The term "knives" is employed herein to denote both those producing smooth cuts and also lines of perforations. In accordance with the different formats of the blanks, preferably in the form of bag blanks, webs of paper or plastic must be provided with transverse cuts and more especially with transverse perforation cuts or lines at different distances apart. There is consequently a need for a way of setting knife rolls to different formats rapidly and simply.